*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
#main{
    width:100%;
    height:408px;
    background:white;
    border:2px solid gray;
    margin:0 auto;
    overflow:hidden;
}
h2{
    text-align:center;
}
#con{
    width:100%;
    height:400px;
    position:relative;
    top:-408px;
    border-collapse:collapse;
}
.row{
    height:100px;
    width:100%;
}
.cell{
    height:100px;
    width:25%;
    float:left;
    border:rgb(54,74,129) 1px solid;
}
.black{
    background:black;
}
.btn{
    width:100%
    text-align:center;
}
.start{
    display: block;
    margin:20px auto;
    width:150px;
    height:50px;
    border-radius:10px;
    background:yellowgreen;
    line-height:50px;
    color:#fff;
}